1. Field of the Invention
This present invention relates to a membrane electrode assembly of a solid polymer electrolyte fuel cell, in particular, which has a high initial performance and a superior durability.
2. Description of Related Art
In recent years, a fuel cell are anticipated as a means of reducing global warming and environmental disruption and a solution to energy problems, and thus research and development on fuel cells is being enthusiastically conducted. A fuel cell uses hydrogen gas as a fuel gas and generates energy by an electrochemical reaction of hydrogen and oxygen, and there are various types of fuel cells including a phosphoric acid fuel cell, a molten carbonate fuel cell, a solid electrolyte type fuel cell, and a solid polymer electrolyte fuel cell. Among these, a solid polymer electrolyte fuel cell can start operation at room temperature and can also provide higher output with small configuration, and thus receives attention as a power source for two-wheeled or four-wheeled vehicles, or portable power supply.
In this solid polymer electrolyte fuel cell, the basic structure unit is a membrane electrode assembly, which is sandwiched between separators to make a single cell and then combined with several tens to hundreds of single cells to be used as a stack (battery). The membrane electrode assembly, which is the basic structure unit, is formed from these two electrodes that are anode (fuel) and a cathode (air) electrode, and a polymer electrolyte membrane sandwiched by these two electrodes. Both electrodes are formed from a catalyst layer that is close against the polymer electrolyte membrane and conducts oxidization/reductive reaction, and a gas diffusion layer close against this catalyst layer. The catalyst layer allocated to both electrodes is formed from an ion conductive material, and a catalyst that is a metal is supported by an electrical conductive material such as carbon. The solid polymer electrolyte fuel cell that is formed from components like these supplies the anode electrode side with fuel including hydrogen, and generates electricity by supplying the cathode electrode side with oxygen or air.
Conventionally, a solid polymer electrolyte fuel cell has a problem in that the performance is decreased by long-term use. The first factor to decrease the performance is that catalyst activity is deteriorated by a sintering of the catalyst metal. The second factor is that an oxidization corrosion reaction of a catalyst carrier such as carbon progresses. The third factor is that the deterioration of the gas diffusivity that is caused by crushing electrode of a bearing pressure. For the solution to this problem, a solid polymer electrolyte fuel cell, in which a catalyst layer of a cathode electrode has a Pt—Co catalyst that is Pt—Co alloys supported by carbon, has been suggested thereto(refer to Patent Document 1). This Pt—Co catalyst has an effect that the particle size increase by a sintering of the catalyst is controlled, by alloying platinum and cobalt. Therefore, this Pt—Co catalyst has high catalyst activity compared with the typical conventional used platinum catalyst, so that a solid polymer electrolyte fuel cell having superior power generation performance can be provided.
[Patent Document (1)] Japanese Patent Application Laid-Open No. 2003-142112
However, while catalyst activity is high, this Pt—Co catalyst causes a corrosion of a catalyst carrier such as carbon. Accordingly, by long-term electrical energy generation, the corrosion of catalyst carrier such as carbon progresses causes a deterioration of power generation performance.